Back in the day I worked in a very international environment, two Tunisian colleagues spoke Tunisian to each other, but when the Moroccan or Lebanese guys from the other teams came to ask some questions, everybody switched to French. If was small talk, they would stick to Arabic with the Moroccan though.
It's pretty amazing that Arabic, technically spoken in a contiguous region from Morocco to Saudi Arabia isn't mutually intelligible with itself, whereas English, French or Spanish, separated by oceans for centuries, even if they grew different variants, stay intelligible.